Permutations And Combinations Question 200

Question: If $ ^{n}P _{r} $ = 720. $ ^{n}C _{r}, $ then r is equal to [Kerala (Engg.) 2001]

Options:

A) 6

B) 5

C) 4

D) 7

Show Answer

Answer:

Correct Answer: A

Solution:

  • $ ^{n}P _{r}=720.{{}^{n}}C _{r} $
    Þ $ ^{n}P _{r}\div {{}^{n}}C _{r}=720 $
    Þ $ r!=720=6! $
    Þ r = 6.

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